This invention relates generally to mattress foundation structures. More particularly, this invention relates to a box spring assembly of the typed which utilizes non-coil springs.
Box spring assemblies using non-coil springs have been known since 1964, the first such spring assembly known to applicant being disclosed in U.S. Pat. No. 3,286,281. Box spring assemblies of this general type are advantageous with respect to conventional box spring assemblies using coil springs because they provide a stiffer foundation for the mattress and contain a reduced amount of spring wire. These box spring assemblies are also advantageous from standpoints of prolonged service life, ease of assembly, and cost of manufacture.
Mattress foundation structures which utilize non-springs, often referred to as wire forms, are also known. Examples of this type of mattress foundation are disclosed in U.S. Pat. Nos. 4,377,279 and 5,052,064. Non-spring or wire form mattress foundation structures, when used in cooperation with a mattress, offer increased stiffness and support. This is especially desirable around the perimeter of the foundation structure. As such, the non-spring mattress foundation structure prevents significant localized deflection of the mattress and mattress foundation when a person is sitting on the edge of the bed. This in turn eliminates the "sliding off" feeling typically associated with less stiff or soft mattress foundations and box spring assemblies.
While the non-spring mattress foundation structures exhibit benefits with respect to perimeter stiffness, they also exhibit an inherent limitation as a result of this increased stiffness. While not being apparent during normal use conditions, this limitation can arise under "normal" abuse conditions. Examples of normal abuse conditions, as this term is used herein, would include impact loads resulting from a person jumping, diving or falling onto the bed. The increased load applied to the bedding foundation under an abuse condition, coupled with the limited deformation resistance of the non-spring structure, often results in the non-spring structure acquiring a permanent set and being permanently damaged.
It is an object of the present invention to provide a box spring assembly which simulates a non-spring mattress foundation in terms of effective firmness while improving the structure's deformation resistance under normal abuse conditions.
In achieving the above and other objects, the present invention provides for a box spring assembly having a rectangular frame made up of side rails, end rails and a plurality of cross rails. The cross rails are generally parallel to each other and the end rails and are substantially perpendicular to the side rails. A welded wire grid or support deck is supported, generally horizontally, a predetermined distance above the frame. The support deck includes a number of straight wires arranged in criss-cross fashion. The straight wires include long wires, which extend lengthwise of the frame, and cross wires, which extend crosswise of the frame. The support deck also includes a border wire that extends around the perimeter of the support deck so as to substantially correspond with the perimeter of the frame. In addition to defining the perimeter of the support deck, the border wire also supports the long wires and cross wires.
Extending between the support deck and the frame, so as to yieldably support the support deck above the frame, are a number of spring modules or support springs. Each of the support springs is formed of spring wire and has a body made up of two side-by-side yieldable portions. The yieldable portions each include an upper column section and a lower column section connected together by a middle section. The middle section is configured so that it will bend in a substantially vertical plane in response to downwardly directed loads thereby providing the box spring assembly with the desired deformation resistance.
The yieldable portions of the support springs are unitarily formed and connected together at their upper ends by a mounting bar which extends therebetween. The mounting bar coacts with at least one of the straight wires to secure the support spring to the support deck. The lower ends of each yieldable portion are provided with a mounting foot that is attached to the frame to secure the support spring in its position.
When provided as described above, the middle sections will bend in response to a load being applied to the support spring. The middle sections provide a break in the straight line of the upper and lower column sections enabling the support spring to resist normal abuse conditions without developing a permanent set. In preferred form, the middle sections are arcuate and generally semi-circular in shape. This avoids any area of stress concentration that might weaken the support springs during bending in response to an applied load.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the append claims taken in conjunction with the accompanying drawings.